There is evidence that caffeine makes people more susceptible to attitude change, but
what drives this effect is unclear. We studied the effects of caffeine and mood on attitude
change, heart rate (HR), and brain activity (measured with electroencephalography—
EEG). Participants received caffeine or a placebo and viewed positive, neutral, or
negative pictures from the International Affective Picture System (IAPS), which are
standardized for valence and arousal. Participants then read persuasive arguments for
implementing senior comprehensive exams at a nearby institution. Attitudes about such
exams were taken before the study and after the participant read the persuasive argument.
EEG and HR were recorded before and after caffeine consumption and picture viewing.
Unexpectedly, HR decreased in the caffeine condition and increased in the placebo
condition, suggesting that withdrawal affects HR more than caffeine itself in caffeine
users. Although the caffeine manipulation failed to produce an attitude change in this
study, our HR findings suggest that previously reported caffeine-facilitated attitude
change may actually have been due to relief from withdrawal effects that were present in
the placebo condition. Also in the present study, negative IAPS images decreased selfreported
mood, but there were no other effects on mood or arousal. In general, cognitionrelated
brain activity increased (high alpha activity decreased and beta activity increased)
after the persuasive argument, especially toward the back of the head. However, the
caffeine and mood manipulations produced more complex interactions.

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Kelly Ann Coney granted permission for the digitization of her paper. It was submitted by CD.